Disease mechanisms in myofibrillar myopathy (MFM): We have generated knock-in mice reproducing ZASP/LDB3 A165V, A147T and R268C mutations. The A165V mice were generated using conventional recombineering method in collaboration with Dr. Shyam Sharan (NCI). Preliminary data on the A165V mice show pathological changes reminiscent of human zaspopathy. We have established the experimental group to examine the disease progression in these mice over the course of 1-year. The A147T and R268C mice were generated using CRISPR-Cas9 approach and are currently into F2/F3 generation. The A147T and A165V mutations cause a similar late-onset MFM phenotype involving skeletal muscle, heart and peripheral nervous system in patients. The R268C mutation causes primarily neurogenic disease in patients. We are also developing BAG3 P209L knock-in mice using CRISPR-Cas9 method. This BAG3 mutation in patients cause severe early-onset MFM affecting skeletal muscle, heart and peripheral nervous system. Identifying shared molecular and cellular pathways in the mouse models of ZASP- and BAG3-related MFM would be key to better understanding of the disease mechanisms in MFM overall as ultimately all gene defects lead to the same morphological changes of the Z-disc disruption, actin cytoskeleton dissolution and accumulation of myofibrillar degraded products. There is a growing interest from patient community to develop therapeutics for MFM. Our goals are to define the molecular and cellular targets in these mice for therapeutic development in MFM. The mouse models will be useful in preclinical treatment trials to test therapeutics. Early experimental data suggests that there is abnormal gain-of-function disease mechanism. We plan to collaborate with Dr. Carsten Bonnemann and his team for resources and guidance in regards to developing precision medicine therapeutics (for example, RNA-based allele silencing) which can be ultimately applied to patients. At the protein level, we have completed in vitro characterization of ZASP-actin interaction in collaboration with Dr. Paul Wingfield (NIAMS) (published in 2017). We are decorating F-actin with purified ZASP to examine ZASP-actin complex with cryo-EM (with Greg Alushin, NHLBI). We have completed our studies of ZASP and other MFM proteins in the nervous system (manuscript in preparation) in prelude to our mouse model studies. Patient studies: We completed the MRI analysis of the NIH Duchenne muscular dystrophy (DMD) Imaging study (11-N-0261) and published the results in 4 manuscripts during the year. We completed all study visits in the myotonic dystrophy (DM) clinical research network study (DMCRN; 14-N-132). We have begun the data analysis of the ankle dorsiflexion strength and myotonia measurements by the ankle intellistretch device (developed at the NIH). The data analysis of all 6 participating sites is expected to begin in Fall-Winter 2017. We have developed a novel hand-held device to measure hand grip myotonia and the pilot study to characterize the device in DM1 patients is expected to begin in September 2017. We plan to continue our clinical research in DM1 patients with the goal of characterizing the respiratory failure in the disease and better define the clinical endpoints for the upper extremity function (part of this work will be in collaborations with DMCRN sites). We plan to begin natural history studies in MFM patients with ZASP, BAG3 and other subtypes to better define clinical endpoints and biomarkers for disease progression in clinical trials..